1. Field of the Invention
This invention relates in general to a vertical cavity surface emitting laser (VCSEL). More particularly, the invention concerns a VCSEL that uses electrical contact layers integrated into the laser cavity of the device.
2. Description of Related Art
There are many applications of lasers which require emission at wavelengths which are traditionally difficult to achieve, particularly the green and blue regions. The applications which call for wavelengths in these regions fall mostly into two broad categories, those that require coverage over the visible spectrum and those which are resolution-driven. Applications which call for coverage over the visible spectrum include display technologies, including projection displays and visual screens, such as television screens. Applications which are resolution-driven take advantage of increased spatial resolution afforded by shorter wavelengths. For example, optical data storage media, such as compact discs and laser discs require a focused laser beam to read the data off the disc. If shorter wavelengths are used, then data storage densities can be increased.
Various approaches to fabricating blue lasers, including gas lasers, and frequency-shifted solid state lasers have been attempted. However, it is a commonly held opinion that blue laser sources will only enjoy widespread use if they can be made inexpensively, for example using semiconductor fabrication techniques, and be made to operate reliably.
In recent years, the vertical-cavity semiconductor laser (VCL) has emerged as a new coherent light source alongside the conventional in-plane semiconductor laser. Advantages of the VCL include its compactness, inherent single-longitudinal mode operation, circular beam profile and straightforward integration with other electronic circuitry. Vertical-cavity lasers hold promise of superior performance in many optoelectronic applications and lower manufacturing cost than in-plane lasers.
State of the art GaAs-based vertical-cavity lasers operate continuously at room temperature with sub-100 .mu.A threshold currents. The outstanding performance of these lasers is partly due to their monolithic fabrication process and the quality of Al(Ga)As/GaAs quarter-wave mirrors, which are presently the highest quality epitaxial mirrors that can be routinely fabricated.
It is therefore desirable to combine the advantages of VCL lasers with new semiconductor materials to produce blue and green semiconductor lasers.
Semiconductor diode lasers operating in the infrared have been very successful and attempts have been made to produce lasers operating in the blue and green regions of the spectrum from semiconductor materials. Attempts have been made using II-VI semiconductor compounds, such as zinc sulfide. However, II-VI-based semiconductor lasers manifest severe problems with reliability and lifetime.
An alternate approach using the group III nitrides has emerged as the most promising approach for generating green, blue, and even ultraviolet light. There are, however, certain difficulties with this approach also, including the formation of doped regions to form a diode junction.
Therefore, there is a need for blue and green semiconductor lasers which can be fabricated inexpensively and reliably, which demonstrate good beam qualities, and which avoid the problems of doping the III-N semiconductor compounds to form diode junctions.